1. Field of the Invention
The present invention relates to printers in which a shuttle is driven in reciprocating fashion by a rotatable cam, and more particularly to arrangements in which the rotatable cam is motor driven through a flywheel, the cam surface is oiled, and a counterbalance assembly is driven in reciprocating fashion by the cam in opposition to the shuttle.
2. History of the Prior Art
Printers are known in which a rotating cam is employed to reciprocate a shuttle. An example of such a printer is provided by U.S. Pat. No. 3,941,051 of Barrus et al., PRINTER SYSTEM, which patent issued on Mar. 2, 1976 and is commonly assigned with the present application. In the printer described in the Barrus et al. patent, a motor is coupled via a drive belt to rotate a flywheel which in turn is coupled to a cam. The cam engages a shuttle at one side thereof and a counterbalance assembly at an opposite side thereof. Engagement of the shuttle and the counter-balance assembly by the cam is effected through cam follower assemblies. The cam drives the shuttle and the counter-balance assembly in opposing reciprocating fashion. In this manner, movement of a mass within the counterbalance assembly is out of phase with movement of the shuttle assembly and counterbalances the shuttle assembly to thereby greatly minimize shaking and other vibratory motion within the printer.
Further examples of printers of the type shown in U.S. Pat. No. 3,941,051 of Barrus et al. are provided by copending application Ser. No. 069,486 of Farb et al., PRINTER HAVING INTERCHANGEABLE SHUTTLE ASSEMBLY, and copending application Ser. No. 069,021, Farb et al., PRINTER HAVING IMPROVED HAMMERBANK, both of which were filed Jul. 1, 1987 and are commonly assigned with the present application. The Farb et al. applications describe improved printers of the type disclosed in the Barrus et al. patent, such printers having readily interchangeable shuttle assemblies, improved hammerbanks and various other improved features. However, reciprocating shuttle motion is still carried out in such arrangements by a cam driven through a flywheel and also engaging a counterbalance assembly.
Printers of the type described in the Barrus et al. patent and the Farb et al. applications typically employ a counterbalance assembly which includes a mass in the form of a block of generally rectangular configuration having a cam follower assembly mounted within the block at one end thereof so that the cam follower of the assembly protrudes from the block and engages the cam. A spring disposed between a fixed reference and an opposite end of the block biases the block to maintain constant engagement of the cam follower with the cam. In such counterbalance arrangements, the block or other mass is typically mounted for reciprocating movement by one or more generally horizontally disposed shafts mounted on the housing for the printer and received within linear bearings in the block. Typically, the shafts must be spaced apart from the common axis through the cam and the cam followers of the counterbalance assembly and the shuttle, resulting in rotational and other components of force being applied to the linear bearings in addition to linear forces. Moreover, even where one or more shafts are located along or at least relatively close to the common axis, play within the linear bearings receiving such shafts is such that a tendency of the bearings to bind on the shafts is a constant problem. Moreover, the presence of the bearings and the shafts is an item of expense which may be further aggravated by the periodic need to replace the bearings and/or the shafts.
Accordingly, it would be advantageous to provide a counterbalance assembly in which the block or other mass is mounted for generally linear, reciprocating motion by a relatively inexpensive and simple arrangement which eliminates the need for linear bearings and shafts.
In the printers of the type described in the Barrus et al. patent and the Farb et al. applications, it is necessary that the surface of the cam be kept lubricated with a thin film of oil. This is normally accomplished by a wick positioned so as to contact the surface of the cam and provided with a quantity of lubricating oil. The wick bears against the rotating cam so as to replenish oil as necessary to maintain a film of the lubricating oil on the cam surface. However, such wicks which are typically made of fabric have been found to periodically dry out, requiring they be frequently examined and oil added thereto as necessary. If the wick nevertheless dries out prematurely or otherwise inadvertently, the lubricating film of oil on the cam surface will dissipate and this may result in erratic shuttle driving as well as premature wearing of the cam followers and the cam itself. Moreover, even where the wick is kept well oiled, the nature of the wick is such that a less than uniform film of oil may be maintained on the cam surface.
Accordingly, it would be desirable to provide a cam oiler which is capable of applying a relatively uniform, thin coating of lubricating oil to the cam surface and thereafter maintaining such lubricating film for a substantial period of time without the need for replenishing the oil in the oiler.
In printers of the type described in the Barrus et al. patent and the Farb et al. applications, the presence of a flywheel of substantial mass in conjunction with the cam is necessary because of the rather substantial inertia of the shuttle and the counterbalance assembly. Typically, the drive motor for the cam is coupled via a drive belt to a flywheel, with the flywheel being mounted on a common shaft with the cam. The drive motor rotatably drives the flywheel which in turn rotates the cam while at the same time imparting sufficient momentum to overcome the problems posed by the relatively high inertia of the shuttle and the counterbalance assembly. However, such driving arrangement occupies considerable space within the printer as well as adding to the expense of the printer because of the need for the separate motor, the flywheel and the drive belt therebetween. The presence of the drive belt coupling the motor to the flywheel introduces a further maintenance factor in terms of such things as wear and the occasional need to replace the drive belt.
Accordingly, it would be advantageous to provide a cam driving arrangement which is of more compact configuration and which eliminates the need for a drive belt or similar coupling between the motor and the flywheel.